Storing and utilizing data used in activities of a corporation have been practiced. For example, data such as operation logs of a manufacturing unit in an assembly line of a product is stored to be used for improvement of manufacturing processes. Moreover, when comparison analysis is performed with a plurality of trend graphs by superimposing waveforms thereof with each other, displaying a first waveform and a second waveform with an enlarged or a reduced display time range, with a fixed relative positional relationship of the first waveform and the second waveform has been proposed (Japanese Laid-open Patent Publication No. 2009-104502).
However, for example, when a graph is created using a time axis in each process in an assembly line of a product as a vertical line, and changes of the product being manufactured as a horizontal line, the trace graph that indicates the changes of the product lies flat if a displayed time range is enlarged. Accordingly, it is difficult to distinguish differences in angle formed by trace graphs corresponding to respective products relative to the time axis, and it is difficult to grasp a problem occurring in the assembly line.